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80m Dipole problems

Discussion in 'Amateur Radio Antennas' started by BenMara, Aug 22, 2018.

  1. BenMara

    BenMara W9WDX Amateur Radio Club Member

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    So i have a 80m dipole fed with 150' of 450ohm window line. Its up at 50' i can NOT get it to tune on 20m with my Palstar AT4K.
    Same antenna less elevation will tune 80m through 6m on a Dentron Super Tuner..

    No idea what else to do.


     

  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    I had a hard time getting my 80m doublet to tune on both 80m and 20m and ended up adding in about 20 extra feet of feedline and even I had to play wih the length of the dipole itself. I had a remote auto tuner outside the house and ran coax cable from it back to the shack.
     
    The DB likes this.
  3. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    Ben: The AT4K is a Differential "T" design tuner...finding the "sweet" spots can be a little tricky.
    First the button marked coax/balanced must be in Bal...Other point is the roller counter works kinda in reverse. The higher number on the counter is actually the lower inductance setting. See the manual for best starting points. I tune mine by watching the power out and then adjust the caps as you see power increase your getting closer..then adjust the roller "slightly" and adjust caps again "slightly" otherwise you will go right past the sweet spot. The "T" circuit once tuned correctly is actually a more efficient circuit....BUT does take time to get correct.
    Keep playing with it and as you find the sweet spot write the numbers down and when you change bands it will give you a relative spot to start tuning next time.
    All the Best
    Gary

    And yes: sometimes I have had to add a short piece of extra line...Like CK said to get one stubborn band to tune...Couple 3 ft will do it...I have a short stubb off the tuner and just wire nut it in/out of the line...to get that one band to come in...sounds silly but will make the difference.
     
    #3 BJ radionut, Aug 22, 2018
    Last edited: Aug 22, 2018
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  4. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    Ben: Here's a thought also...the AT4K does need to have 12vdc on during operation...otherwise the control relays will not operate.
    All the Best
    Gary

    Also Ben...How long are the legs of your 80m antenna...I have mine cut 62.5ft each side...my preferred tuner is my double "L" it tunes it great all bands...I had excellent success with a Link Coupled tuner(Like Johnson Matchbox) also...plus a Dentron MT2000A with the massive 4:1 Balun or the Dentron 3K Monitor tuner...
    The AT4K seems to give me good performance but in reality I would trade it for a PALSTAR BT1500 or another Johnson KW Matchbox if the deal came along...I think the AT4K works better on coax feed antennas or Inverted "L" types due to the adjustable input tuning circuit, than balanced line but just MHO...as far as general ease of operation goes...They are built like TANKS...2KW++ and they just smile and go one. I have used mine with a Inverted "L" antenna (160 thru 20m) hooked to a good counterpoise and it ROCKS...MHO on balanced line it is problematic to tune...Once you get it tuned correctly it Rocks!...But patience is required:LOL:...that is just the nature of the "T" circuit IMO:whistle:
     
    #4 BJ radionut, Aug 22, 2018
    Last edited: Aug 22, 2018
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  5. BenMara

    BenMara W9WDX Amateur Radio Club Member

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    Yea the has a been a tank since purchase. Long ago had a 80m dipole fed with 600ohm could tune that one anywhere.... with the AT4K....
    I have been thinking about a Palstar BT1500, but the QA of Palstar has been going down hill. Maybe i can get my hands on the Dentron tuner.
     
  6. BenMara

    BenMara W9WDX Amateur Radio Club Member

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    A local offered me the Dentron tuner.... :)
     
  7. Road Squawker

    Road Squawker Sr. Member

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    compare both antennas at the same height or same tuner at different antenna heights on one antenna.

    change one thing at a time when you are troubleshooting.

    been there, done that, and I have the shirt.:D
     
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  8. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    RS is correct...just the minor change in Elevation, may have altered the overall impedance of the antenna to make that happen on certain bands...Tricky stuff sometimes.:confused::mad:
    All the Best
    Gary
     
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  9. BenMara

    BenMara W9WDX Amateur Radio Club Member

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    Antenna mentioned was my previous HF antenna that knocked down during a storm. Its now with a New Ham Operator. Looks like i scored a Dentron tuner.

    Im currently making another 80m 450 ohm fed dipole...
    any suggestions other then avoid 33’, 66’ and 165’ feed line lengths?
     
  10. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    Ben: To be quite honest I never measured the feedline. To me the the best length was whatever reached the tuner comfortably...Plus a little extra so that it never gets taught even in the wind. I bring it almost straight down about 30ft, short piece of cotton rope to a 4 x4 so it swings with the wind, tied thru the window center...Then about 25-30ft to another short piece of rope which keeps it about 2ft below my gutters and then it's about 15ft to my PVC 1" conduit thru the outside wall right below the gutters down to the tuner on top self of my bench stack(y)
    All the Best
    Gary
     
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  11. 543_Dallas

    543_Dallas Sr. Member

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    You can get unlucky and end up with a very high impedance at the tuner. This can cause arcing if you run a cheap tuner with an even cheaper balun built in. Low impedance causes heating and wastes power. That doesn't stop people from making contacts but still sucks.

    You can't just avoid certain ladder line lengths without considering the length of the antenna. You need to have an idea of what the feed point impedance of the antenna is on each band. Then remember that even 1/4 wave multiples of feedline will give you the same impedance at the tuner and odd 1/4 wave multiples will transform the impedance from low to high, or vice versa.

    Who ever came up with the ladder line lengths to avoid need to give you a dipole length to use when you are avoiding them. Otherwise it's false information .

    My favorite solution is a home made balanced L. If you use a variable cap rated for high voltage it will take anything you throw at it. A coax choke goes on the 50 ohm (input) side of the tuner. There's no balun being used on the output where the impedance can vary drastically on different bands. It's an easy project but I'll spare the details unless you are interested.
     
    Shadetree Mechanic likes this.
  12. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Change only one thing at a time! Drag racing will teach you that. Make a change take a test run. Keep track of your result. If things improve dramatically change it just a little more at at time until it peaks. Then move on to your next adjustment.
    I have seen people change a dozen things at a time and the performance drops to the point where a kid on a tricycle will drag their butts.
    Patients and small changes will get you to the peak!
     
    binrat likes this.
  13. DainBramage

    DainBramage Well-Known Member

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    well, for starters, I would consider 300 ohm feedline and about 130 (+/-) feet of wire.

    Or even better roll your own 600 ohm
     
  14. JoeDirt

    JoeDirt Well-Known Member

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    I had a problem tuning 80m on mine, tried different lengths of feed line.

    You do not need a resonate antenna on 80m, mine was around 25 ohms at 3.550mhz, my tuner didnt like 25ohms....

    I ended up lengthening my dipole to an overall length of 140' which moved my resonate frequency to around 3 mhz. Now I do not have any tuning issues.
     
  15. BenMara

    BenMara W9WDX Amateur Radio Club Member

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    So here is an update. Same 80m dipole 100' 450 ohm Plastar AT4K will tune only 80m and 40m. Dentron Tuner will tune 80m, 20m, 17m, 15m.
    Im going to take my Both Tuners, meters and radio to front porch and see if it has anything to do with where it enters the house.

    The saga continues... But i did get US Virgin island and Spain on 80m DX window...
     

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